1. Field of the Invention
The present invention generally relates to an apparatus and a process for removing ceramic materials from, and cleaning the surfaces of, articles and specifically relates to improved apparatus and processes for removing ceramic material and cleaning loose and tightly bound contamination from the surfaces of airfoil components on a production basis.
2. Description of the Prior Art
U.S. Pat. No. 5,685,917 to Sangeeta entitled “Method for Cleaning Cracks and Surfaces of Airfoils”, U.S. Pat. No. 5,643,474 to Sangeeta entitled “Thermal Barrier Coating Removal on Flat and Contoured Surfaces” and U.S. Pat. No. 5,779,809 to Sangeeta entitled “Method of Dissolving or Leaching Ceramic Cores in Airfoils” explain the use of an organic caustic mixture under pressure for the cleaning and removal of ceramic materials such as ceramic cores used in the production of casting gas turbine hardware and thermal barrier coatings used to improve the temperature capabilities of gas turbine hardware. The processes outlined have several problems that must be overcome to practice the technology in production environments with higher throughput. Basically, the patents describe methods of attacking the ceramic materials by exposing them under elevated temperature and pressure to organic caustic solutions comprised of a volatile organic compound, a caustic compound and water.
The reagents involved are highly alkaline and flammable, a combination that renders them particularly difficult to handle. The pressures and temperatures set forth in these patents are high, being elevated well above ambient, thereby causing the entire process to be extended in duration. While this is acceptable for laboratory settings or in small scale runs, it is undesirable in production settings. These prior art processes comprise loading a pressure vessel such as an autoclave, with soiled, coated turbine hardware and adding the caustic reagents. The loaded pressure vessel is brought to the appropriate elevated temperature and pressure, thereby subjecting the coated parts to the caustic reagents which act on the hardware to remove the coating. The pressure vessel is then cooled and depressurized and the stripped hardware is removed from the vessel. The hardware is then removed from the vessel and residual reagents are removed from the hardware. However, these prior art processes are not readily adaptable for the high volumes usually encountered in production situations. The prior art processes do not address the problems of adapting such autoclave equipment, typically designed for batch processing, for continuous production processing. Nor do the prior art processes address the problems encountered in reusing these contaminated and dangerous chemicals.
What is needed are equipment and methods capable of removing ceramic materials such as coatings from coated hardware as the first step in a process for refurbishment and restoration of turbine hardware in an efficient and safe manner, while eliminating contamination from the reagent to allow reuse.